Other automakers have been penalized in recent years for putting a rosy spin on fuel economy figures.

Korean carmakers Hyundai(HYMTF) and Kia agreed to pay a combined $100 million fine in the U.S. in 2014 for overstating fuel economy estimates for many of their vehicles. They also had to refund customers for the difference in estimated fuel costs.

That same year, Ford(F) said it would compensate owners of about 200,000 U.S. vehicles after discovering the cars' gas mileage was overstated.